If you've ever written an ontology in RDF/XML using a text editor, certainly you wanted to poke out your own eyes. Lately I've taken to writing ontologies by hand in TextMate (awesome Mac code editor) in N3 or Turtle syntax, with syntax highlighting. Should I consider Manchester syntax or another serialization format instead? Am I crazy for editing ontologies by hand? Using Protege is liking creating ontologies using training wheels.

You're not crazy, just eccentric :) Actually, I typically write my RDF by hand as well (Turtle or TriG syntax, using VIM with syntax highlighting). But to be honest, I usually only do this for models of "managable" size (where "managable" is a function of how many other users have to co-edit, the number of classes and relations, and the number of OWL restrictions I need). For more complex stuff I tend to use TopBraid Composer.

At the time we switched from Protege to TopBraid, this was not so much because TopBraid provided more features, it was born out of frustration with Protege's instability (we got a lot of crashes and data loss). That was several years ago though, I hear Protege has improved a lot since then. But apart from that, TopBraid is a great tool with a host of useful features (UML'ish visualisation, rule- and query support, to name just two).

I guess the easiest syntax is the one you are more confortable with. It is a question of taste but also of tools. For instance, using RDF/XML can be convenient because most text editors have some built-in XML-related functionalities. I personally edit my ontologies in RDF/XML in a text editor, and I'm quite confortable with it (no joke!). But I admit that RDF/XML is cumbersome and I tend to use Turtle when it comes to communicating examples (in emails, forums, semanticoverflow, etc). Now there is an official OWL/XML syntax [1] which is probably quite nice but I've not yet taken the time to look at it in details. You can take a look at a screencast showing how OWL/XML plays nicely with XML tools [2].

I personally prefer Turtle for writing stuff by hand, for editing it I've recently written my own editor - named simply rdfEditor - which I hope to release in the next month or so. It provides syntax highlighting, auto-completion, validate as you type and various export features.

There is a screencast at http://www.youtube.com/watch?v=upY-Vpte8OI but the quality is rather iffy as I didn't have a very good video capturer/mic to make it with (looks best at 1080p full screen and is somewhat unviewable at standard resolutions)

It will be open source as part of my dotnetrdf project, you can browse the source on sourceforge at http://dotnetrdf.svn.sourceforge.net/viewvc/dotnetrdf/Trunk/Utilities/rdfEditor/ - obviously you can do a anonymous checkout of the repository to get it